Motor-fan unit for moving wet working air

ABSTRACT

In an electric motor fan unit for environments such as washing machines, vacuum cleaners, air samplers, a motor section frame enclosing an internal motor cooling air path includes an end bracket with an enlarged rim for mounting fan shell and interior partition structures defining a fan section housing for a smaller motor ventilating impeller and a larger working air centrifugal impeller commonly mounted on the motor shaft outboard of the motor section frame and drawing respective air streams into housing axial inlets for discharge at the housing circumference. Back-to-back and axially spaced impeller dispositions and corresponding housing structures and also resultant direction of ventilating air from the motor to the air discharge region ensure both adequate motor and adjacent bearing ventilation and bearing protection from working air borne moisture, contaminants, and high temperature and humidity, by simple, low cost, durable structure.

nited States Patent 1 91 Porter et al.

[54] MOTOR-FAN UNIT FOR MOVING WET WORKING AIR [75] Inventors: John II. Porter, Talmadge, Ohio;

Robert 0. Swift, Stow, both of Ohio [52] [1.5. CI. ..417/424, 415/98, 417/423 R [51] Int. Cl ..F04b 35/04 [58] Field Of SBalCIl ..417/427, 423 R, 424,

[56] References Cited UNITED STATES PATENTS 2,767,904 10/1956 Doyle ..4l7/424 2,822,122 2/1958 C016 ..417/424 2,822,123 2/1958 C016 417/424 3,177,731 4/1965 Peterson... .....308/77 3,303,995 2/1967 Boeckel.... .....415/79 3,341,113 9/1967 Sebok ..310/62 2,731,194 1/1956 Kent ..417/312 1,230,206 6/1917 Niemeyer ..4l7/423 A X 2,474,439 6/1949 Segesman ..3l0/62 X 1 May 15, 1973 2,726,807 12/1955 Lewis ..417/423AX 7 Primary Examiner-William L. Freeh Assistant Examiner-John F. Winburn Attorney-Ely, Golrick & Flynn V [57] ABSTRACT In an electric motor fan unit for environments such as washing machines, vacuum cleaners, air samplers, a motor section frame enclosing an internal motor cooling air path includes an end bracket with an enlarged rim for mounting fan shell and interior partition structures defining a fan section housing for a smaller motor ventilating impeller and a larger working air centrifugal impeller commonly mounted on the motor shaft outboard of the motor section frame and drawble structure.

14 Claims, 4 Drawing Figures MOTOR-FAN UNIT FOR MOVING WET WORKING AIR Though discussion and description here is presented mainly in terms of vacuum cleaner motor fan units, it is to be understood that described inventive features may find use in other applications of the motor fan unit.

In modern vacuum cleaners of various types, commonly the fan system for pumping or moving the vacuum cleaning air stream, the so-called working air, and the electric motor therefor, generally a commutating series universal type motor, are fabricated as a unit to be assembled into the overall appliance, that is, as a motor fan unit, because of various considerations relating to overall cost, facility of production, fabrication and maintenance, and'as well because of the mechanical interrelation of the fan system and motor system wherein dynamic balance of the rotating parts is required.

Because of heat generated under the general and normal operating conditions, the motor must be cooled by a ventilating air stream positively moved, rather than relying upon convection or radiation.

In many priorart structures, all or part of the working air has been directed to the motor section either in reaching the air intake of, or in discharging from, the main working fan section; 'but various disadvantages attendant upon such systems have led to use of a separate motor ventilating fan to move a cooling air stream separate and distinct from the working air and of structures to define a ventilating air flow path or paths through the motor structure.

Generally speaking such separate ventilating fan has been mounted on'the motor shaft at a location axially between the bearings within the main motor housing or frame, though at times outboard of one or the other end bearing in enclosure means usually partially defined by part of the motor frame structure. Prior expedients for thispurpose have generallyinvolved structure or fabrication operations entailing additional cost of parts, and/or inconvenienceor cost in assembly, testing and balancing.

Especially where the motor fan units may be called upon to handle not only dry air, that is, carrying merely the water vapor of the ambient atmosphere, but also wet working air streams, as where the vacuum cleaner unit is operated on wet floors or shampooed carpeting,

for example, further problems arise. First, the use of the working air as ventilating air obviously would be unsuitable not only for the reasons which have lead to abandonment of such system even where fdryoperations" solely are contemplated, but also because of the potential motor damage by-moisture, and as well danger of shock to a user, unless special and costly preventative expedients are used in the motor structure.

Further even where a separate ventilating air stream is used, there still exists a hazard especially to the motor bearing at the fanward end of the unit, where the working. air is wet, as a portion of the contained water may find its way along the shaft and through shaft accommodating housing openings, ultimately to the bearing and even beyond into the motor interior, unless special structural precautions are taken to provide effective sealing between the shaft and surrounding housing or shell structures to prohibit moisture or water access to the bearing. Previous solutions to these problems generally have required structure or manufacturing operations involving costs of additional parts, and/or inconvenience or costs in assembly.

Moreover, the fact that the working temperature of the air often may be rather high engenders a further problem both generally for bearing cooling adjacent the fan section and as well through the possibility of temperature accelerated bearing deteriorating action of the moisture.

It is the general object of the present invention to provide a motor fan unit of relatively low cost and of simple and rugged structure (as compared to the prior art devices of similar performance and life ratings), wherein the motor is ventilated or cooled by an air stream other than the working air stream.

It is a further object of the present invention to provide a motor fan unit wherein, by relatively simple and low cost expedients, there is afforded to the fanward end bearing protection against damage by moisture, detergents, or other substances brought into the motor fan unit by the working air.

It is a still further object of the present invention to provide a simple arrangement whereby the motor section ventilating fan and the direction of the cooling air stream path serve not only for motor cooling, but also for protection of the fanward end bearing against damage by workingair borne water and other materials.

Other objects and advantages will appear from the following description and the drawing wherein:

FIG. 1 represents a motor fan unit embodying the present invention, shown partially in elevation and partially in longitudinal section;

FIG. 2 is a fragmentary longitudinal sectional view I indicating a variation of FIG. 1;

FIG. 3 is a fragmentary longitudinal section representing a modification of the invention; and

FIG. 4 is a fragmentary longitudinal section indicating a variation of FIG. 3.

In the drawings, FIG. 1 shows a motor fan unit incorporating the invention comprising a motor section designated as a whole by the general reference letter M, including a stator structure S, and rotor R having a shaft 1 l; and a fan section designated as a whole by the general reference character F, including a main or working air suction fan or impeller I mounted on the rotor shaft and enclosed in a fan shell or housing as hereinafter more fully described.

In the motor section M, here shown as a commutating motor, the stator structure includes a first or fanward motor and bracket casting 12, to the left end of which a second end bracket casting member 13 is secured by bolts 14 passed through arcuate rim slots in 13 to provide, for the brush holder structures 15 carried on 14, an angular adjustability relative to the field core and winding assembly 17 secured in member 12.

The shaft 11 of the commutating armature is sup ported by appropriate bearings 19 and 20 in bearing sockets of respective integral spider portions bridging the open ends of members 13 and 12, the latter of which enlarges through radial wall 12a into an integral cylindrical rim portion 12b supporting the fan section housing shell and partition members 23 and 25 as hereinafter described.

As evident in the drawing, the left end bracket member 13 provides an open structure permitting cooling air to enter into the motor section both around the bearing socket supporting bridge portion of 13, and around the brushes and commutator, and thence to flow lengthwise both between the wound field structure and the rotor or armature on the one hand and on the other externally between the field structure and the enclosing motor frame housing formed by members 12 and 13, as permitted by longitudinal passages formed by clearances arising by the external shape of the field, particularly in its core or lamination stack.

The structure thus far described in detail may be considered to be conventional.

At the fan section, a main fan shell 23 is a drawn sheet metal cup-shaped member having a generally flat disk-like radial end wall 23a centrally apertured to provide an axial vacuum intake air inlet 23b. Member 23 includes a generally cylindrical wall 230 with one end rounding into 230 and the other mounted on the exteriorly cylindrical rim portion 12b of motor end bracket 12, by being telescoped in a press fit upon the somewhat necked-down right end of a cylindrical wall portion 25c providing effectively a continuation of wall 230 in a similar drawn sheet metal cup-shaped member 25 providing a partition 25a.

The member 25, which here provides an innermost end wall of the fan section housing, at 250 may be either merely press fitted onto 12b up against the integral circumferential stop rib 12f or further secured by a local staking, as at 25s, into an underlying rim groove.

Again the flat radial wall 25a has a central opening 25b defining, for the motor ventilating air, an outlet from the motor section and an inlet into the fan chamber to the motor ventilating air impeller V. The fan shell or impeller housing thus defined by members 23 and 25 is provided with discharge outlet means on its circumference, either a semi-scroll type outlet or as here shown a circumferential series of equi-spaced, louver-like openings 23d formed in wall 230 for air discharge.

On the portion of shaft 11 projecting to the right through the bearing into the fan section housing, a spacer sleeve 26 bearing endwise against the inner bearing race at 20, in turn axially located by engagement with a shaft shoulder, through a disk-like flange 26a supports the main body disk 28 of the ventilating fan centrifugal impeller V and the similar body disk 29 of main fan or working air centrifugal impeller I clamped thereagainst in back-to-back relation by clamp washer 30 and a clamping nut 31 threaded onto the extreme shaft end.

The two impellers I and V here are, per se, of generally conventional form and structure, as, for example, made from sheet metal; in V comprising a second annular disk 28d with central opening defining the impeller air intake, and a series of appropriately shaped vanes or blades 28b with opposite end edges secured to 28d and 28; and in the impeller I comprising series of blades 29b and the annular disk 29d forming the intake opening to which the working or cleaning air flows through the inlet 23b in the housing outer wall 23a.

It will be observed that the ventilating impeller V has a diameter markedly smaller than the main impeller I, also that the series of air discharge apertures 23d are axially offset toward the partition means 23, away from the discharging periphery of impeller I. This structure with the known offset of the discharge apertures from I by virtue of the smaller diameter of V additionally minimizes noise effects and conduces to efficiency, while yet permitting sufficient ventilating air flow for motor cooling and other desirable purposes.

With this arrangement, and so also those of the other subsequently described figures, it is apparent that, apart from the motor ventilating fan, the essential motor components are all included as a basic subassembly in the motor section, and that no particular special structure must be included in the motor section components for accommodation of the ventilating fan. Obviously these arrangements may be utilized in multistage fan units, for example, in a two-stage unit where aperture 23b is the second stage inlet, with stationary vanes on the right face of wall 23a; and with another cup-shaped member, similar to 25, pressed onto the end of 23 in the manner of 23 on 25, to enclose a first stage impeller, like to and similarly spaced by a sleeve from I and clamped on a longer shaft extension.

Particularly noteworthy, in the event moisture is carried by the main working air stream entering at 23b during operation of the fan unit, there is no opportunity for such air to bring entrained water droplets or even warm moist air, often occurring with high humidity and temperature, anywhere near the fanward bearing region of the motor section, since the motor ventilating air stream discharging through 25b into impeller V not only functions for the motor and bearing cooling, but also in effect serves as an air curtain over the entire region of its path, from the bearing on out through the space between the exposed inboard side of impeller l and wall 25a, to the discharge outlets 23d thus screening the motor end the, bearing and partition 25a not only from entrained water but also moist warm air.

In the variation of FIG. 1, shown by fragmentary FIG. 2, the cylindrical wall portion 23c of fan shell 23 is press fitted and/or, if desired, staked directly onto the motor end bracket member rim 12b, while the inner partition, which with member 23 defines the impeller chamber, takes the form of a centrally apertured slightly conical disk 35, having an axially inwardly offset rim portion 35r of narrow U-shaped cross section providing a nearly cylindrical flange 35f pressed within the rim 12b, to the extent limited by stop lip 35p. The two impellers I and V are clamped similarly to FIG. 1, the spacer 36 with headed or flanged portion 36f to aid clamping, merely being shortened.

The modification of FIG. 3 is identical to the motor fan unit of FIG. 1 in the motor section, and further, except as hereinafter described, in the fan section in the general structure of the two cup-shaped members 23 and 25 and in their mounting relations to each other and to the rim structure 12b of the adjacent motor end bracket, but differs by including a partition disk member 35, and in the disposition of the impellers V and I, though the latter are both outboard of the motor frame as in FIG. 1. Moreover, member 35 in its own structure and in its manner of mounting to the fan bracket end member rim 12b is identical to the like numbered member in FIG. 2.

In this modification, the ventilating fan impeller V is disposed axially separately from impeller I in the distinct ventilating fan chamber defined between members 35 and 25, impeller V being axially located on the shaft again by the end flange 36fof a shortened spacer 36 (similar to that in FIG. 2), and thereon clamped by a spacer bushing 40 (in diameter substantially equal to the clamping flange 36]) serving in turn to locate the impeller I secured as previously by clamping washer 30 and nut 31 threaded onto the shaft outer end.

Here the central opening in end wall a is reduced in diameter as compared to that in FIG. 1 to a close running clearance with the spacer 40; and further a circular series of equi-spaced holes 25v provide ventilating air discharge outlets from the ventilating impeller chamber, into the space between impeller I and wall 25a in the main or working air impeller chamber, to flow outwardly as previously for a common circumferential discharge through the circumferential series of louvers 23d with the working air peripherally discharged from impeller I. This arrangement, with the apertures 25v for the ventilating fan chamber discharge, uses simpler structure and parts as contrasted with the variation indicated in FIG. 4, wherein the cylindrical wall portion 250 is provided with a set of discharge louvers or openings 25d, such as those at 23d in member 23.

By the modification of FIGS. 3 and 4, again the motor section itself does not incorporate any fan or impeller structures of the unit, which all are located rather in the fan section. Further the working air stream is well separated and screened from the nearby end of the motor and the corresponding bearing, while the ventilating air path within the main fan chamber (FIG. 3) again serves to help sweep droplets of water or other material entrained in the working air out the principle discharge as well as screening the partition 25 in great part from working air contact and attendant heat transmission. The close clearance between 25 and 40 also generally minimizes the chance of water entry into the ventilating fan chamber for approach along the shaft toward the bearing. To the degree that water might pass wall 25a, especially with FIG. 4, the body disk of impeller V serves as an obstruction to moisture travel along the shaft region, slinging any liquid outwardly for discharge with ventilating air through apertures 25d.

Though in the arrangements where the partition means includes, in addition to the innermost housing end wall, an intermediate wall defining inner and outer chambers respectively for the ventilating fan and working air discharging impeller, usually it is preferred to have the described close-running clearance between the intermediate wall aperture and the shaft structure (that is, the spacer sleeve in these embodiments of FIGS. 3-4), yet for some applications the intermediate wall aperture may be notably larger, for example, approaching the diameter of the ventilating impeller, because of the effective bearing screening provided by the rest of the structure and the air streams or paths resulting.

Also it is to be understood that though sheet metal constructions are shown and described for the impellers, main fan housing shell, and the further elements providing the named partition means supported by the end bracket rim, one or more of these may be molded of plastic as suitable for particular applications. For example, in FIG. 3, the cylindrical wall portions 25c and 230 and the intermediate wall 25a may obviously be molded as one piece, bolted or bonded to the rim 1217; with a separate plastic or formed sheet metal disk then applied to the outer end of the molded piece to provide the end wall 23a.

We claim:

1. In an electric motor fan unit, including an electric motor section having motor frame structure supporting and enclosing rotor and stator structure with motor ventilating air passages defined therethrough from a ventilating air inlet to a motor frame portion at one end open for discharge of ventilating air, said frame structure at said one end including a motor end bracket having therein a bearing for the rotor shaft extending therethrough and having an end rim portion with ventilating air discharging open frame areas around the locus of the bearing, and said unit further including a fan section having therein at least one main working air impeller clamped outboard on the shaft portion extending through said bearing and a fan housing structure including housing shell means providing an end wall centrally apertured to form an axial working air inlet to said main impeller and a further wall circumferentially surrounding the said main impeller, said'housing shell means having therein main air outlet means and having an open end supported on said end rim portion, that improvement comprising:

partition means mounted to said rim portion and forming an inmost end wall of said housing structure, said inmost end wall centrally apertured providing around said shaft an axial inlet to said housing for ventilating air discharging from said motor section; and a centrifugal ventilating air impeller secured on said shaft between said main impeller and said inmost end wall; said impellers being separate impeller units secured back-to-back on the shaft in a common chamber defined between the said end walls and with the impeller inlet openings facing the respective said axial inlets, whereby ventilating air and working commonly discharge through said main air outlet means. 2. An electric motor fan unit improvement as described in claim 1 with said main air outlet means offset away from the periphery of the main impeller toward said inmost wall, and said ventilating air impeller having a smaller diameter than said main impeller, whereby ventilating air discharging from the smaller impeller sweeps the space between said inmost wall and the working air path of discharge to said main outlet means. 3. An electric motor fan unit improvement as described in claim 1, with said partition means provided by a cup-shaped member having a short cylindrical wall portion fitted and secured on the exterior of said rim portion and a generally radial, centrally apertured wall portion as said inmost end wall, and said housing shell having its open end fitted over the cylindrical wall portion of the last said member and thereby secured to said rim portion.

4. An electric motor fan unit improvement as described in claim 1, with said partition means provided by a centrally apertured disk-like member forming said inmost end wall and secured to said end bracket and circumferentially sealing to said rim portion, and said housing shell means having said open end fitted on the said rim portion. 5. An electric motor fan unit improvement as described in claim 1, including a spacer sleeve on said shaft, with one end abutting a part of said bearing axially fixed on and rotating with said shaft and having on its other end a radial flange supporting portions of said ventilating and main impellers centrally apertured for successive reception of the shaft, and clamping nut means threaded onto the outboard shaft to clamp said impellers against the said flange. 6. In an electric motor fan unit, including an electric motor section having motor frame structure supporting and enclosing rotor and stator structure with motor ventilating air passages defined therethrough from a ventilating air inlet to a motor frame portion at one end open for discharge of ventilating air, said frame structure at said one end including a motor end bracket having therein a bearing for the rotor shaft extending therethrough and having an end rim portion with ventilating air discharging open frame areas around the locus of the bearing, and said unit further including a fan section having therein at least one main working air impeller clamped outboard on the shaft portion extending through said bearing and a fan housing structure including housing shell means providing an end wall centrally apertured to form an axial working air inlet to said main impeller and a further wall circumferentially surrounding the main impeller, said housing shell means having therein main air outlet means and having an open end supported on said end rim portion, that improvement comprising:

partition means mounted to said rim portion and forming an inmost end wall of said housing structure, said inmost end wall centrally apertured providing around said shaft an axial inlet to said housing for ventilating air discharging from said motor section; and a centrifugal ventilating air impeller secured on said shaftbetween said main impeller and said inmost end wall, further separate partition means supported on said rim portion and providing a centrally apertured intermediate wall dividing said housing structure into an outer, main impeller chamber and an inner, ventilating air impeller chamber, means supporting said ventilating impeller in the respective said chamber axially spaced outboard from said bearing, and spacer sleeve means supporting said meain impeller spaced on said shaft from said ventilating impeller and located in the other said chamber, and clamping nut means threaded onto the outboard shaft end to clamp the last said impeller. 7. An electric motor fan unit improvement as described in claim 6, with the said further partition means provided by a member having a short cylindrical wall portion with an open end secured on the said rim portion and a generally radial, centrally apertured wall portion as said intermediate wall, and said housing shell means having its open end secured on the cylindrical wall portion of the last said member and thereby supported on said rim portion.

8. An electric motor fan unit improvement as described in claim 7, with the first said partition means provided by a centrally apertured disk-like member as said inmost end wall and having a circumferential flange of narrow ushaped cross section press-fitted into said rim portion. 9. An electric motor fan unit improvement as described in claim 7, wherein the cylindrical wall of said further partition means is provided with a plurality of equi-spaced apertures for discharge of air from the ventilating air impeller chamber. 10. An electric motor fan unit improvement as described in claim 7, wherein said ventilating air impeller has a smaller diameter than the main impeller, and said intemiediate wall is provided with a circular series of apertures spaced outwardly of the periphery of the ventilating air impeller as air outlets for the ventilating impeller chamber to the main impeller chamber, whereby ventilating air and working air streams discharge commonly from the main impeller chamber through said main air outlet means. 11. An electric motor fan unit improvement as described in claim 10, with said main air outlet means comprising a circumferential series of spaced air outlet apertures adjacent said intermediate wall in the cylindrical wall portion of said housing shell, said main impeller spaced axially from the intermediate wall beyond the locus of the last said series, and said circular series located radially between the peripheries of said impellers, whereby ventilating air discharging from the ventilating impeller chamber sweeps the space between said intermediate wall and the working air path of discharge to said main impeller outlet means. 12. An electric motor fan unit improvement as described in claim 6, wherein the aperture of said intermediate wall has a'close running clearance with said spacer sleeve means extending therethrough. 13. In an electric motor fan unit, including an electric motor section having motor frame structure supporting and enclosing rotor and stator structure with motor ventilating air passages defined therethrough from a ventilating air inlet to a motor frame portion at one end open for discharge of ventilating air, said frame structure at said one end including a motor end bracket having therein a bearing for the rotor shaft extending therethrough and having an end rim portion with ventilating air discharging open frame areas around the locus of the bearing, and said unit further including a fan section having therein at least one main working air impeller clamped outboard on the shaft portion extending through said bearing and a fan housing structure including housing shell means providing an end wall centrally apertured to form an axial working air inlet to said main impeller and a further wall circumferentially surrounding the said main impeller,

said housing shell means having therein main air outlet means and having an open end supported ported on a cylindrical formation on said rim portion; said partition means secured at the external circumference thereof to said rim portion and including a centrally apertured disk-like member as said on said end rim portion, that improvement comprising:

partition means mounted to said rim portion and forming an inmost end wall of said housing struc- 10 ture, I said inmost end wall centrally apertured providing around said shaft an axial inlet to said housing for ventilating air discharging from said motor sec- 7 tion; and a centrifugal ventilating air impeller se- ,cured on said shaft between said main impeller and said inmost end wall; said housing shell means comprising a cup-shaped member integrally providing the end wall having said axial working air inlet and a cylindrical wall for circumferentially surrounding said main iminmost end wall and having a circumferential flange of narrow U-shaped cross section press fitted into said portion. 14. An electric motor fan unit improvement as described in claim 13, wherein said partition means further includes a cup-shaped member with open end fitted on said rim portion and providing a centrally apertured intermediate wall dividing said housing structure into an outer, main impeller chamber and an inner, ventilating air impeller chamber, and means supporting said ventilating and main impellers in the respective said chambers axially successively spaced from said bearing; said housing shell having its open end fitted on the peller, cylindrical wall portion of the last said member and said cylindrical wall having therein said main air thereby supported on said rim portion.

outlet means and having its open end sup UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF PATENT NO. 3,733,150

DATED I May 15, 1973 INVIENTOR(S) John H. Porter and Robert 0., Swift It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 29, for "end the, bearing" read --end, the

bearing.

Column 6, line 38, for "working" read --working air--.,

Column 7, line 58 (57 by actual count) for "meain" read -main-.

gigned and Scaled this twent -th'd [SEAL] y D y 0f December1975 A ttest:

:UTH- C. MASON C. MARSHALL DANN trestmg Ojfrcer (mnmissiunir oj'larents and Trademarks 

1. In an electric motor fan unit, including an electric motor section having motor frame structure supporting and enclosing rotor and stator structure with motor ventilating air passages defined therethrough from a ventilating air inlet to a motor frame portion at one end open for discharge of ventilating air, said frame structure at said one end including a motor end bracket having therein a bearing for the rotor shaft extending therethrough and having an end rim portion with ventilating air discharging open frame areas around the locus of the bearing, and said unit further including a fan section having therein at least one main working air impeller clamped outboard on the shaft portion extending through said bearing and a fan housing structure including housing shell means providing an end wall centrally apertured to form an axial working air inlet to said main impeller and a further wall circumferentially surrounding the said mAin impeller, said housing shell means having therein main air outlet means and having an open end supported on said end rim portion, that improvement comprising: partition means mounted to said rim portion and forming an inmost end wall of said housing structure, said inmost end wall centrally apertured providing around said shaft an axial inlet to said housing for ventilating air discharging from said motor section; and a centrifugal ventilating air impeller secured on said shaft between said main impeller and said inmost end wall; said impellers being separate impeller units secured back-toback on the shaft in a common chamber defined between the said end walls and with the impeller inlet openings facing the respective said axial inlets, whereby ventilating air and working commonly discharge through said main air outlet means.
 2. An electric motor fan unit improvement as described in claim 1 with said main air outlet means offset away from the periphery of the main impeller toward said inmost wall, and said ventilating air impeller having a smaller diameter than said main impeller, whereby ventilating air discharging from the smaller impeller sweeps the space between said inmost wall and the working air path of discharge to said main outlet means.
 3. An electric motor fan unit improvement as described in claim 1, with said partition means provided by a cup-shaped member having a short cylindrical wall portion fitted and secured on the exterior of said rim portion and a generally radial, centrally apertured wall portion as said inmost end wall, and said housing shell having its open end fitted over the cylindrical wall portion of the last said member and thereby secured to said rim portion.
 4. An electric motor fan unit improvement as described in claim 1, with said partition means provided by a centrally apertured disk-like member forming said inmost end wall and secured to said end bracket and circumferentially sealing to said rim portion, and said housing shell means having said open end fitted on the said rim portion.
 5. An electric motor fan unit improvement as described in claim 1, including a spacer sleeve on said shaft, with one end abutting a part of said bearing axially fixed on and rotating with said shaft and having on its other end a radial flange supporting portions of said ventilating and main impellers centrally apertured for successive reception of the shaft, and clamping nut means threaded onto the outboard shaft to clamp said impellers against the said flange.
 6. In an electric motor fan unit, including an electric motor section having motor frame structure supporting and enclosing rotor and stator structure with motor ventilating air passages defined therethrough from a ventilating air inlet to a motor frame portion at one end open for discharge of ventilating air, said frame structure at said one end including a motor end bracket having therein a bearing for the rotor shaft extending therethrough and having an end rim portion with ventilating air discharging open frame areas around the locus of the bearing, and said unit further including a fan section having therein at least one main working air impeller clamped outboard on the shaft portion extending through said bearing and a fan housing structure including housing shell means providing an end wall centrally apertured to form an axial working air inlet to said main impeller and a further wall circumferentially surrounding the main impeller, said housing shell means having therein main air outlet means and having an open end supported on said end rim portion, that improvement comprising: partition means mounted to said rim portion and forming an inmost end wall of said housing structure, said inmost end wall centrally apertured providing around said shaft an axial inlet to said housing for ventilating air discharging from said motor section; and a centrifugal ventilating air impellEr secured on said shaft between said main impeller and said inmost end wall, further separate partition means supported on said rim portion and providing a centrally apertured intermediate wall dividing said housing structure into an outer, main impeller chamber and an inner, ventilating air impeller chamber, means supporting said ventilating impeller in the respective said chamber axially spaced outboard from said bearing, and spacer sleeve means supporting said meain impeller spaced on said shaft from said ventilating impeller and located in the other said chamber, and clamping nut means threaded onto the outboard shaft end to clamp the last said impeller.
 7. An electric motor fan unit improvement as described in claim 6, with the said further partition means provided by a member having a short cylindrical wall portion with an open end secured on the said rim portion and a generally radial, centrally apertured wall portion as said intermediate wall, and said housing shell means having its open end secured on the cylindrical wall portion of the last said member and thereby supported on said rim portion.
 8. An electric motor fan unit improvement as described in claim 7, with the first said partition means provided by a centrally apertured disk-like member as said inmost end wall and having a circumferential flange of narrow u-shaped cross section press-fitted into said rim portion.
 9. An electric motor fan unit improvement as described in claim 7, wherein the cylindrical wall of said further partition means is provided with a plurality of equi-spaced apertures for discharge of air from the ventilating air impeller chamber.
 10. An electric motor fan unit improvement as described in claim 7, wherein said ventilating air impeller has a smaller diameter than the main impeller, and said intermediate wall is provided with a circular series of apertures spaced outwardly of the periphery of the ventilating air impeller as air outlets for the ventilating impeller chamber to the main impeller chamber, whereby ventilating air and working air streams discharge commonly from the main impeller chamber through said main air outlet means.
 11. An electric motor fan unit improvement as described in claim 10, with said main air outlet means comprising a circumferential series of spaced air outlet apertures adjacent said intermediate wall in the cylindrical wall portion of said housing shell, said main impeller spaced axially from the intermediate wall beyond the locus of the last said series, and said circular series located radially between the peripheries of said impellers, whereby ventilating air discharging from the ventilating impeller chamber sweeps the space between said intermediate wall and the working air path of discharge to said main impeller outlet means.
 12. An electric motor fan unit improvement as described in claim 6, wherein the aperture of said intermediate wall has a close running clearance with said spacer sleeve means extending therethrough.
 13. In an electric motor fan unit, including an electric motor section having motor frame structure supporting and enclosing rotor and stator structure with motor ventilating air passages defined therethrough from a ventilating air inlet to a motor frame portion at one end open for discharge of ventilating air, said frame structure at said one end including a motor end bracket having therein a bearing for the rotor shaft extending therethrough and having an end rim portion with ventilating air discharging open frame areas around the locus of the bearing, and said unit further including a fan section having therein at least one main working air impeller clamped outboard on the shaft portion extending through said bearing and a fan housing structure including housing shell means providing an end wall centrally apertured to form an axial working air inlet to said main impeller and a further wall circumferentially surroundiNg the said main impeller, said housing shell means having therein main air outlet means and having an open end supported on said end rim portion, that improvement comprising: partition means mounted to said rim portion and forming an inmost end wall of said housing structure, said inmost end wall centrally apertured providing around said shaft an axial inlet to said housing for ventilating air discharging from said motor section; and a centrifugal ventilating air impeller secured on said shaft between said main impeller and said inmost end wall; said housing shell means comprising a cup-shaped member integrally providing the end wall having said axial working air inlet and a cylindrical wall for circumferentially surrounding said main impeller, said cylindrical wall having therein said main air outlet means and having its open end supported on a cylindrical formation on said rim portion; said partition means secured at the external circumference thereof to said rim portion and including a centrally apertured disk-like member as said inmost end wall and having a circumferential flange of narrow U-shaped cross section press fitted into said portion.
 14. An electric motor fan unit improvement as described in claim 13, wherein said partition means further includes a cup-shaped member with open end fitted on said rim portion and providing a centrally apertured intermediate wall dividing said housing structure into an outer, main impeller chamber and an inner, ventilating air impeller chamber, and means supporting said ventilating and main impellers in the respective said chambers axially successively spaced from said bearing; said housing shell having its open end fitted on the cylindrical wall portion of the last said member and thereby supported on said rim portion. 